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Developing a fast, sensitive and convenient method for the detection of hydroxyl radicals ( OH) in the atmosphere could help us know the precursor levels of atmospheric species and control air pollution. In this work, the carbon fiber paper (CFP) functionalizing with a kind of covalent organic frameworks (COFs), formed from 1,3,5-triformylphloroglucinol (Tp) and benzidine (BD) (COF(TpBD)), was firstly used a new platform for .OH trapping and detection. The COF(TpBD) modified CFP was acted as a filter to impregnate salicylic acid (SA) and a detector to detect 2,5-dihydroxybenzoic acid (2,5-DHBA) which was produced from the reaction between the impregnated SA and .OH in the atmosphere. This method provided a linearity for 2,5-DHBA from 5.0 × 10-14 mol/L 1.0 × 10-9 mol/L with a detection limit of 6.9 × 10-15 mol/L, which is corresponding to the amount of .OH from 3.0 × 107 to 6.0 × 1011 molecules/cm3 with the detection limit of 4.1 × 106 molecules/cm3. This COF(TpBD)-CFP platform has been successfully applied for the detection of .OH concentration under different conditions of Yangzhou when the sampling time was shortened to 30 min. This work has provided a new method for atmospheric OH detection with excellent sensitivity, simplicity, and high speed.